Arrangement for multistage audio amplification



May 6, 1930. w. MOSER ARRANGEMENT FOR MULTISTAGE AUDIO AMPLIFICATION Filed April 6, 1925 INVENTOR WILHELM MOSER 16 M TTORNEY Patented May 6, 1930 STATES PAllill l l WILHELM MOSER, OF BERLIN, GERMrhNY, ASSIGNOR TO GESELLSCHAFT Fill-It DBAHT- LOSE TEIJEGRAPHIE Iii. B. Ii, OF BERLIN, GERIVIANY ARRANGEMENT FOR IYZULTIEZTAGE AUDIO AMPLIFICATION Application filed April 6, 1925, Serial No. 20,886, and in Germany April 7, 1924.

My invention relates to radio apparatus and more particularly to systems known as audio amplifier systems. It has for its object to provide an audio amplifier system which will be free, to the lowest possible degree, from noises and howling due to back-coupling be tween the various tubes.

Other objects will be apparent from the following specification and claims when considered with the accompanying drawing in which the single figure represents an embodiment of my invention.

In audio or low frequency multi-stage amplification, as is well known, disturbances are frequently caused by the undesirable capacitative coupling between the different tubes. Hence, care must be taken so that the capacitance between the individual tubes will be as small as feasible. Now, according to the invention the coupling of the grid circuits of the tube next above with the anode circuit of the tube next below is to be effected by the use of a series arrangement of two transformers. in this manner the total capacitance existent between the two coupled tubes is substantially reduced, since the same consists of the series arrangement of two capacitances.

Referring to the drawing, the reference characters and 30 represent electron discharge tubes of a usual and well-known type. Each tube comprises an anode, a filamentary :athode and a grid all enclosed in an evacuated envelope.

The A-batteries 18 and 19 provide energy to heat the cathodes of the tubes 10 and 30 respectively. The B'bat-teries 20 and 21 supply the necessary plate or anode currents for these tubes. The incoming audio frequencies are applied at the terminals 1 and E2. whence they are conducted to the grid and cathode of the first amplifier tube 10. In the plate circuit of tube 10 is included primary winding 12 of the audio frequency transformer 11. The secondary of the audio frequency transformer 1.1 is connected to the primary 15 of the second audio frequency transformer 14. The secondary 16 of the transformer 14 is connected to the grid and f lament of the second amplifier tube 30. The terminals 31 and 32 represent the output terminals of the amplifier and may be connected to any suitable signal responsive apparatus, as, for instance, an ordinary telephone receiver (not shown).

The tube 10 amplifies the incoming oscillations in the usual manner and the transformer 11 conveys these oscillations into the intermediate circuit A whence they are conveyed through transformer 1a to the input circuit of tube 30, which, by its ordinary amplifier action, amplifies these oscillations to a still greater extent.

Across the coils 13 and 15 of transformers 11' and ll may beconnected a variable and low ohmic resistance 17 whereby the power or energy to be supplied from one tube to the other tube can be varied, so that the relationship, between internal and external resistance requisite in order to realize best amplification is obtainable.

The ratio of transformer 11 may be such that it steps down the voltage in going from tube 10 to tube 30, while the ratio of transformer 14 may be such that it steps up the voltage in going in the same direction.

It will easily be seen that the capacity between the tubes 10 and due to the transformer windings and as represented by the condensers 3, l, 5 and 6 (shown in dotted lines) is much less than would be the case if only one transformer were used. This is due to the well-known principle that condensers of a given capacity connected in series have a less resultant capacity than either condenser taken alone.

Having described my invention, I am entitled to all modifications thereof as fall fair- 1y within the scope of the following claims:

1. The combination of two adjacent amplifying tubes and an audio frequency coupling between said tubes, said audio frequency cou pling comprising two audio frequency transformers and a circuit connecting said transformers in series for reducing the capacity coupling between said amplifying tubes.

2. The combination of two adjacent amplifying tubes and an audio frequency coupling between said tubes. said coupling comprising two transformers, one connected to the output of the first amplifying tube and the other connected to the input of the second amplifying tube, and anuntuned circuit connecting the secondary of the first mentioned transformer and the primary of the last mentioned transformer in series.

3. The combination of two adjacent amplifying tubes and audio frequency coupling between said. tubes, said audio frequency coupling comprising a transformer connected to the output of one of said tubes a second transformer connected to the input of the other of said tubes, a circuit connecting said transformers in series and means connected across said circuit for varying the energy supplied from one tube to the other.

4. The combination of two adjacent amplifying tubes and an audio frequency coupling between said tubes, said audio frequency coupling comprisin a transformer connected to the output of one of said tubes, a second transformer connected to the input of the other of said tubes, an untuned circuit connecting said transformers in series and an impedance element connected across said circuit in shunt relation to said transformer.

5. The combination of two adjacent amplifying' tubes and an audio frequency coupling between said tubes. said audio frequency coupling comprising a transformer connected to the output of one of said tubes, a second transformer connected to the input of the other of said tubes, a circuit connecting said transformers in series and a resistance element connected across said circuit in shunt relation to said transformers.

6. The combination of two adjacent amplifying tubes and an audio frequency coupling between said tubes, said audio frequency coupling comprising a transformer connected to the output of one of said tubes, a second transformer connected to the input of the other of said tubes, a circuit connecting said transformers in series and a low ohmic resistance connected across said circuit in shunt relation to said transformers.

7. The combination of two adjacent thermionic repeaters and an audio frequency coupling between said repeaters, said audio frequency coupling comprising two audio frequency transformers and an untuned circuit connecting said transformers in series for reducing the capacity coupling between said between said tubes, said audio frequency coupling comprising two audio frequency transformers, a circuit connecting said transformers in series, and a variable impedance connected across said circuit in shunt relation to said transformers.

DR. WILHELM MOSER. 

